Secondary bladder and rectal cancer risk estimates following standard fractionated and moderately hypofractionated VMAT for prostate carcinoma

Abstract

Purpose: To estimate the risk for bladder and rectal cancer induction due to standard fractionated (SF) and moderately hypofractionated (HF) volumetric modulated arc therapy (VMAT) for prostate carcinoma. Methods: Twelve patients with low or intermediate-risk of prostate cancer referred for external-beam radiotherapy were included in this study. Three computed tomography-based VMAT plans were created for each study participant. The first plan was generated by assuming patient's irradiation with SF-VMAT (78 Gy in 39 fractions). The second and third plans were created on the basis of two different HF schedules (HF-VMAT 1 : 70 Gy in 30 fractions, HF:VMAT 2 : 60 Gy in 20 fractions). Data from differential dose-volume histograms obtained by the above treatment plans were employed to calculate the organ equivalent dose (OED) of the bladder and rectum with the aid of a nonlinear model accounting for fractionation and proliferation effects. The calculated OED values were used to estimate the average lifetime attributable risk (LAR av ) for the appearance of radiotherapy-induced secondary bladder and rectal malignancies. The lifetime risk of radiation carcinogenesis was compared with the respective organ-, and age-dependent lifetime intrinsic risk (LIR) of cancer development for unexposed males. Results: The average OED of the rectum from SF-VMAT, HF-VMAT 1 and HF-VMAT 2 for prostate cancer was 972.0, 900.2, and 815.7 cGy, respectively. The corresponding values for bladder were 73.4, 72.3, and 71.0 cGy. The LAR av for rectal cancer induction varied from 0.06% to 0.4% by the fractionation schedule used for irradiation and by the age of the patient at the time of treatment. The corresponding risk range related to the development of secondary bladder malignancies was 0.06-0.33%. The SF-VMAT, HF-VMAT 1 and HF-VMAT 2 led to an increase of the lifetime rectal cancer risk with respect to LIR by 2.2-9.8%, 2.0-9.1% and 1.8-8.2%, respectively, depending upon the patient's age. The corresponding elevation for bladder cancer induction was up to 8.0%, 7.9% and 7.7%. Conclusions: The use of VMAT for prostate carcinoma leads to a noteworthy increase of the lifetime risk for bladder and rectal cancer induction compared to that of unexposed people irrespective of the patient's age at the time of treatment and the applied fractionation scheme. The cancer risk data presented in this study may be taken into account by radiation oncologists and medical physicists in the selection of the optimal radiation therapy plan.

VMAT for prostate cancer with 6‑MV and 10‑MV photons: Impact of beam energy on treatment plan quality and model‑based secondary cancer risk estimates

“…The lifetime risks of carcinogenesis were estimated from a patient group with a mean age of 68 years subjected to hypofractionated VMAT for prostate carcinoma up to a dose of 70 Gy. Limited information has been published on the probability of developing secondary malignancies from prostate irradiation using hypofractionation schedules (13,22). The cancer risks of the present study are consistent with those of a previous report on hypofractionated treatment with 6-MV photons at the ages of 60 and 70 years (13), reporting lifetime bladder and rectal cancer risks of 0.06-0.18% and 0.07-0.20%, respectively.…”

“…Limited information has been published on the probability of developing secondary malignancies from prostate irradiation using hypofractionation schedules (13,22). The cancer risks of the present study are consistent with those of a previous report on hypofractionated treatment with 6-MV photons at the ages of 60 and 70 years (13), reporting lifetime bladder and rectal cancer risks of 0.06-0.18% and 0.07-0.20%, respectively. Stokkevag et al (22) provided a wide range of bladder and rectal cancer risks of 0.01-0.80% for 60-year-old patients receiving 67.5 Gy to the prostate and simultaneously 60 Gy to the seminal vesicles in 25 fractions with 6-MV VMAT.…”

“…By contrast, the contribution of the neutron dose to the total dose of critical organs becomes significant when radiation therapy is delivered with 15-MV or 18 MV photon beams (20). The DVH parameters of the two plans of each patient satisfied the previously published dose constraints (11,13). The differences in the mean values of the parameters related Table III.…”

“…The dose calculations of the VMAT plans were made using a Monte Carlo algorithm. The dose constraints for the PTV and OARs were based on previous reports (11,13) and they are presented in Table I. Cumulative dose-volume histograms (DVHs) of the aforementioned structures were employed to determine the relevant V i , defined as the percentage of the target or OAR volume absorbing a radiation dose equal to i Gy.…”

Automatic Radiobiological Comparison of Radiation Therapy Plans: An Application to Gastric Cancer

“…The VMAT plans were designed using two complete arcs in opposite directions. The above VMAT planning strategy is used for abdominopelvic tumors in our department [ 14 , 15 ]. Six and ten MV X-rays were used for IMRT and VMAT plans.…”